By Kevin Bunch, IJC
Three swimmers were dragged a half mile out into Lake Erie by a sudden wave in May 2012. In 1954, a 3-meter wave from Lake Michigan appeared out of nowhere and swept anglers off a pier in Chicago, killing seven. These were major examples of meteotsunamis, a type of tsunami created by atmospheric conditions that prove difficult to predict and prepare for.
Meteotsunamis aren’t as well-known as their earthquake-caused tsunami counterparts but occur all over the globe, according to Frank Seglenieks, water resources engineer with Environment and Climate Change Canada. They form when a change of air pressure and jump in wind speed are pushed along by a warm or cold front over the water at the same speed and direction as the water’s own motion. As they keep pace, the water continues to absorb energy from the atmosphere. In the Great Lakes, they tend to form due to large convective storms from the southwestern end of the basin. Lakes Michigan and Erie bear the brunt of that due to their location and water depth, Segleneiks explained.
Meteotsunamis also can become more dangerous through “reflection,” says Eric Anderson, a researcher with the US National Oceanic and Atmospheric Administration (NOAA). Water in the Great Lakes and other enclosed water bodies “sloshes” back and forth over time, raising water on one end of the lake and lowering it at the other before sloshing back again. If the meteotsunami wave hits a shoreline it can reflect back toward the other shore though this process. This happened with the three swimmers in Ohio in 2012, Anderson said, effectively decoupling the tsunami wave from the storm pressure zone that initially sparked it hours before. An enclosed space like a harbor can have its own wave resonance that can superimpose a meteotsunami on other waves if they match up, though that is seen more in the ocean than the Great Lakes.
Some estimates put the frequency of meteotsunami waves in the hundreds per year in the Great Lakes – they form primarily in Lakes Michigan and Erie, occasionally cropping up in Lake Ontario and parts of Superior and Huron – but most of those are either undetectable or only about 2 centimeters (1 inch) in size, Seglenieks said. Any tsunami larger than 30 cm (1 foot) is considered significant, and generally those are reported one to five times a year between all the lakes, according to a 2016 paper. They don’t look like a wave breaking toward the shore as much as a sudden rise in water level followed by a rapid drop.
“The biggest danger is the unexpectedness,” Seglenieks said. “If it’s stormy and windy the instinct is to not go too close to the shore and you might sit back from the pier, but the problem is sometimes they hit during perfectly sunny days in calm waters.”
Developing the ability to issue an advisory when a notable tsunami could form would be helpful for people in populated areas. That was the goal of a June workshop in Ann Arbor, Michigan, hosted by the Cooperative Institute for Great Lakes Research. Attendees sought to identify the information gaps preventing effective forecasts and alerts of meteotsunamis. Doing so requires effective modeling, detection and forecasting for weather and water conditions.
The workshop included representatives of NOAA along with its Great Lakes Environmental Research Laboratory, Department of Fisheries and Oceans Canada, University of Michigan and University of Wisconsin, along with an expert on Mediterranean meteotsunamis from Croatia. Anderson said NOAA has the ability to detect and to an extent forecast storms and their associated atmospheric pressure changes. On the water side of things, wave models in the lakes are limited to forecasting short, choppy waves, and while lake hydrodynamic models, which focus on how fluids move, can forecast a variety of conditions they don’t pick up the meteotsunamis. Researchers discussed methods of using the existing observational infrastructure to improve those models and see if a viable forecasting system can be put together in the next few years.
Seglenieks said since the weather side of things requires such small-scale features to accurately show a tsunami forming, forecasters need good information on current conditions and a knowledge base to build forecasts. The first step is to look at models of previous tsunamis and see what indicators exist for the wave building that can be applied to forecasts.
“It takes a lot of high-resolution weather modeling, basically,” Seglenieks said.
Workshop participants also discussed how best to communicate these forecasts. Anderson said hearing the term meteotsunami may cause people to panic or write it off as nonsense, so attendees talked about an education campaign to explain what meteotsunamis are and how to react them.
Kevin Bunch is a writer-communications specialist at the IJC’s US Section office in Washington, D.C.